Download Database Preservation Issues

Digital Preservation Testbed
Database Preservation Issues
Remco Verdegem
Bern, 9 April 2003
1
Testbed Background
• Established October 2000 by
– Ministry of the Interior
– Ministry of Education, Culture and Sciences
• Dutch National Archives
• Will finish 1st October 2003
• Objective:
– To secure sustained accessibility to reliable
government information in the digital era
2
Research Questions
•
•
•
•
•
Advantages of different preservation approaches?
Factors and effectiveness of each approach?
Basic Requirements for preservation?
Which metadata are essential for preservation?
Options for Attribute preservation?
3
Scope
• 4 Archival Record Types:
–
–
–
–
Text documents
Spreadsheets
Emails
Databases
• 3 Preservation Approaches:
– Migration
– Emulation
– XML
4
Database
• Three components:
– Contents
– Database Management System (DBMS)
– Application
The database system comprises all three
components.
The term database includes at least the contents
of a database.
5
Different types of databases
•
•
•
•
•
Relational - Oracle, Microsoft Access
Hierarchical
Native XML - Tamino
Object oriented
Network
6
Compared to other recordtypes
• Each database system is unique
• The native environment (application) is not widely
available and is generally database specific
• The technical challenge for converting databases
into a preservation friendly format is high
• Operational database contents are subject to
frequent changes
• The relationship between a record and a database
is unclear and is also context dependent.
7
Relationship database & record
• Records are contained, as whole objects, in the
database.
• The contents of the database contain records. Each
record is spread over tables.
• The contents of the database is the record.
• Database data (as whole objects or spread across
tables) accessed or presented in a precise manner
in the application form a record.
• The whole database system is the record
8
• A database is not a record at all
What are we trying to preserve?
• The record/s as discrete, easy to access entities.
• The ability to reconstruct the contents of the
database.
• The data and input/output screens to
form/reproduce records.
• The whole database system.
9
Dutch archival regulation
• article 6e
“for databases: the original storage format or ASCII
(flat file, with separator tokens), accompanied by
documentation, preferably as an XML-DTD, about
the structure of the database (at least encompassing
the complete logical data model with a description
of the entities); queries should be stored in the query
language SQL (SQL2)”.
10
Our work so far
• Focus on relational databases.
• Conversion of databases to XML, concentrating on
content and structure.
• Review of commercial tools for converting
databases to XML.
• Design and development of conversion tool.
11
XML; pros
• Open standard, widely accepted and applied, well
structured.
• Platform and program independent.
• Practical approach to the concept of separation of
content, structure and apperance.
• Extensible and controllable; readable by both
humans and machines.
• Free - i.e no royalties payable.
• Widely used, so lots of software tools already
available.
12
XML; cons
• Verbose; indeed human readable, but too much to
read!
• XML will be superseded in 5 or 10 years.
• Complex material -> much pioneering work is still
to be done.
• What to do with the XML?
Alternatives:
 Original file format
 ASCII
13
XML vs migration
• Migration needs to have both systems running.
• Migration needs to happen every few years.
• Lot of work involved in migration; requires
specialist knowledge.
• Conversion to XML can be seen as an intermediate
step in a migration between a present day and a
future database.
• By converting to XML, you remove the dependency
on the present day database system.
14
Tool; how it works
• Concentrates on the data in the database.
• Designed to closely follow the structure of the
relational database.
• One XML file for each table.
• Separate overview XML file.
• Constraint information in the overview file
describes the structure of the database.
• (Optionally) store database views.
15
Problems encountered
•
•
•
•
JDBC or a ODBC/JDBC bridge
Details are different for different databases
Not all of the methods in java.sql work in all cases
Oracle data tables for one application are typically
associated with a particular table owner
• Resources
• Images
16
Demonstration ………
17
Conclusions
• Preservation of databases is still “uncharted
territory”.
• Lot of questions, just a few answers.
• XML is able to preserve content and structure of
databases.
More information:
http://www.digitaleduurzaamheid.nl
18